Sheer drop in cost is epic, possibly (9)
I believe the answer is:
precipice
'sheer drop' is the definition.
(I've seen this before)
'in cost is epic possibly' is the wordplay.
'in' indicates putting letters inside.
'cost' becomes 'price' (price is a kind of cost**).
'possibly' indicates an anagram.
'epic' is an anagram of 'ecip'.
'price' going around 'ecip' is 'PRECIPICE'.
(Other definitions for precipice that I've seen before include "Sheer cliff" , "(Overhang of) steep cliff" , "Steep rock face" , "Steep cliff face" , "Sheer drop" .)